Hydraulic fluids

ABSTRACT

A hydraulic fluid comprises from 10 to 99% by weight of an ester or mixture of esters, having the general formula:   and/or WHEREIN R is a straight or branched chain alkylene group containing at least 2 carbon atoms, each R1 is the same or different and is an alkyl radical containing from 1 to 4 carbon atoms or a phenyl radical, each R2 is the same or different and is an ethylene, propylene or butylene group, each n is the same or different and is 0 or an integer of from 1 to 3, each R3 is the same or different and is an ethyl or methyl group, each R4 is the same or different and is an ethylene or propylene group and m is an integer and from 1 to 90% by weight of a borate ester, or mixture of borate esters, having one of five specified general formulae, for example:   wherein each R5 is the same or different and is a straight or branched chain alkyl group, each R6 is the same or different and is an alktl group and each p is the same or different and is an integer.

United States Patent Ker et al. 1 Oct. 21, 1975 HYDRAULIC FLUIDS [57] ABSTRACT Inventors: Robert Alan Cameron Colin A hydraulic fluid comprises from 10 to 99% by weight Jo rring both O ondon, of an ester or mixture of esters, having the general for- England mula:

[73] Assignee: Burmah Oil Trading Limited,

London, England 22 Filed: Dec. 14, 1973 R d/ RCO-(R*O);CR [21 Appl. No.2 424,712 COW +OR +OR H H Related US. Application Data [63] Continuation of Ser. NO. 219,504, Jan. 20, 1970,

abandoned.

[30] Foreign Application Priority Data Jan. 21, 1971 United Kingdom 2873/71 wherein R is a straight or branched Chain alkylene July 21, 1971 United Kingdom 34240/71 giouP Containing at least 2 Carbon atoms, each is the same or different and is an alkyl radical containing 52 US. Cl. 252/78; 252/49.6; 252/79 from 1 to 4 Carbon atoms or a P y radical, each R2 51 im. cl. C09K 50/00 is the same or different and is an ethylene, Propylene 58 Field of Search 252/73, 75, 7s, 79, 49.6 or buiylene group, each n is the same or different and is 0 or an integer of from 1 to 3, each R is the same [56] References Cited or different and is an ethyl or methyl group, each R is UNITED STATES PATENTS the same or different and is an ethylene or propylene group and m is an integer and from 1 to 90% by 3,033,963 l0/l9(7)l Erucem. weight of a borate ester, or mixture of borate esters, g y 'gi 5 1 having one of five specified general formulae, for ex- 31635825 1 1972 sdw er et al. 252/78 ample: a 3,637,794 l/l972 Sawyer et a]. 252/78 b; l? 6 3 FOREIGN PATENTS OR APPLICATIONS United Kingdom Primary ExaminerBenjamin R. Padgett Assistant ExaminerDeborah L. Kyle Attorney, Agent, or FirmBacon & Thomas HYDRAULIC FLUIDS I ll wherein R is a straight or branched chain alkylene group containing at least 2, preferably 2 to 8, carbon atoms, each R is the same or different and is an alkyl redical containing from 1 to 4 carbon atoms or a phenyl radical, each R is the same or different and is an ethylene, propylene or butylene group, each n is the same or different and is O or an integer of from 1 to 3, each R is the same or different and is an ethyl or methyl group, each R is the same or different and is an ethylene or propylene group and m is an integer, preferably an integer such that the total number of carbon atoms in the RQ group is from 4 to l2, more preferably 4 to 9 and from 1 to 90% by weight of a borate ester, or mixture of borate esters, having one of the following general formulae:

wherein each R is the same or different and is a straight or branched chain alkyl group, each R is the same or different and is an alkyl group, each p is the same or different and is an integer, q is an integer of from 2 to 6, R is the residue ofa di-or poly-hydroxy organic compound having a number of reactive hydroxy groups equal to q, and each R is the same or different and is the residue of a di-hydroxy organic compound which residue is attached to each boron atom via an oxygen atom.

It is highly desirable that the hydraulic fluids of the present invention have a kinematic viscosity at 40C of not more than 5,000cSt, especially not more than 2,000 cSt. It is also desirable that the hydraulic fluids have a boiling point of at least 260C.

The dicarboxylic acid esters of formula I are described in U.K. Pat. Specification No. 1,083,424. Esters which may suitably be used in the present invention are the succinates, glutarates, adipates, azelates, sebacates, isosebacates and nylonates of methyl, ethyl propyl and butyl oxitol, dioxitol and trioxitol described in U.K. Specification No. 1,083,324, the nylonates, especially di(methyl dioxitol) nylonates, being particularly preferred.

The glycol di-esters of formula [I are known compounds and the preferred glycol di-esters are the glycol dipropionates described in UK. Pat. Specification No. 1249803. It is preferred that the hydraulic fluids comprise not more than 50% by weight of the glycol diesters; the remainder, if any, of the carboxylic acid ester component being the esters of formula 1.

Preferred borate esters for use in the present invention are those in accordance with foregoing formula Ill in which each R contains from 1 to 4 carbon atoms and each R contains 1 to 8. more preferably 1 to 4 carbon atoms. Preferably each integer p is from 1 to 8, more preferably 1 to 4. It is particularly preferred that the total ofthe three integers p is from 5 to 15. Specific examples of such borate esters are:

Tris methyl triethylene glycol borate Tris ethyl triethylene glycol borate Tris methyl diethylene glycol borate Tris ethyl diethylene glycol borate Methyl diethylene glycol ethyl diethylene glycol methyl triethylene glycol borate Butyl diethylene glycol or bis butyl diethylene glycol borates in which the, or each, group {OR }OR not derived from the monobutyl ether of diethylene glycol is derived from the monomethyl or monoethyl ether of dior tri-ethylene glycol Alkyl glycol or his alkyl glycol borates in which the, or each, group -|-OR"-}-,,OR not derived from a monoalkyl ether of a monoglycol is derived from the monomethyl or monoethyl ether of dior triethylene glycol.

The preferred form of R R and p in borate esters according to formulae 1V and V is the same as the preferred R R and p for borate esters according to formula III. The group R can be derived from a glycol or thioglycol, an alkanolamine or alkoxylated alkanola mine or a polyol having from 3 to 6 hydroxy groups. Examples of polyols which may be used include pentaerythritol and sorbitol. Examples of suitable alkanolamines have the formula:

wherein each R is the same or different and is an alkylene group, preferably containing 2 to 4 carbon atoms, r is an integer of from 1 to 10, s is 2 or 3 and R is a hydrogen atom or an alkyl group, preferably containing 1 to 4 carbon atoms. Thioglycols from which R can be derived may be of the formula HO+R"X) ROH wherein t is an integer, preferably from 1 to 10, each X is the same or different and is an oxygen or sulphur atom, at least one X being a sulphur atom, and each R" is the same or different and is an alkylene group containing from 2 to 4 carbon atoms.

However, it is particularly preferred that R is derived from a glycol, q in this case being 2. In this case R has the formula -OR +O,, wherein u is an integer and R is a C alkylene group. When R is derived from a simple glycol, e.g. ethylene glycol or hexamethylene glycol, u will be 1 and in this case R is preferably a C alkylene group. Alternatively R may be derived from a polyoxyalkylene glycol. In this case 11 will be an integer greater than I. Preferably u is an inte ger of from 2 to 4 and R is an alkylene group containing from 2 to 4 carbon atoms.

In the foregoing formulae VI and VII, the group R" is derived from a di-hydroxy compound, which is preferably a glycol. In this case R is more preferably a gly col residue of the formula OR wherein each R is the same or different and is an alkylene group and v is an integer of from 1 to 8. When v is 1, R may be a C alkylene group and R will be derived from. for example, ethylene glycool, propylene glycol or hexamethylene glycol. However, most preferably, R is derived from a polyoxyalkylene glycol and v is an integer of from 2 to 4. In this embodiment R is most preferably a C alkylene group.

The borate esters used in the hydraulic fluids of the present invention are also known compounds, for example, as described in US. Pat. Specification No. 3080412 and U.K. Pat. Specifications Nos. 1232369 and 1232370. Borate esters according to formula III can be prepared by esterifying orthoboric acid with monoethers of oxylalkylene or polyoxyalkylene glycols. The esterification may be carried out by conventional esterification techniques and esterification can be with three moles of glycol monoether per mole orthoboric acid; with one or two moles of glycol monoether fol lowed by esterification with two or one moles respectively of a different glycol monoether or by a threestage process with one mole of each of three different glycol monoethers. The esterification is preferably carried out in a slight excess, e.g. excess, of the glycol monoether (i.e. in excess of the particular molar proportion). For example, in a simple one-stage esterification of l mole of orthoboric acid it is preferred to employ 3.3 moles of the glycol monoether.

Borate esters according to formula IV may be prepared in similar manner by esterification of boric acid with one or more glycol monoethers in the appropriate amounts. The esterification may be carried out using conventional techniques. Similarly borate esters of for mula V may be prepared by conventional esterification techniques. Thus boric acid, preferably orthoboric acid, is esterified with twice the molar quantity of one or more glycol monoethers to yield an intermediate of formula:

The intermediate is then reacted with the appropriate dior poly-hydroxy organic compound, from which the group R is derived.

The borate esters of formula VI and VII may also be prepared by conventional esterification techniques, using the appropriate molar ratios of boric acid and dihydroxy compounds.

After preparation of the borate esters, separation and purification may be carried out in known manner.

The proportion of the borate ester employed in the hydraulic fluids of the present invention may be from 2 to preferably from 2 to 6071 by weight and within this preferred range a wide variety of proportions may be selected. with corresponding adjustment of the dicarboxylic acid ester content. For example, a proportion of from 5 to 20%. e.g. 1071, by weight of borate ester may be used. Alternatively. a proportion of from 40 to 6071. e.g, 45 or 5571, by weight of borate ester may be used.

It will be understood that in addition to the borate and dicarboxylic acid esters of formulae I to VII, the hydraulic fluids of the present invention may contain small amounts of additives conventionally employed in hydraulic fluids.

Typical additives which may be used in the invention are lubricity additives selected from castor oil or castor oil treated in various ways, for example.

Firsts Castor Oil.

Castor oil to Specification DTD72 Blown castor oil, i.e. castor oil blown with air or oxygen while being heated.

Special Pale Blown Castor Oil, i.e. a similarly blown castor oil.

Hydricin 4 i.e. a commercially available ethylene/oxide/propylene oxide treated castor oil. Other lubricity additives which may be incorporated in hydraulic fluids in accordance with the present invention include borate esters e.g. tricresyl borate and phosphorus-containing esters, especially phosphates e.g. tricresyl phosphate.

The hydraulic fluids of the present invention may also include minor proportions of polyoxyalkylene glycols or ethers thereof e.g. those sold by Union Carbide Corporation under the Registered Trade Mark Ucon, particularly those of the LB AND HE series. Suitable examples of these polyoxyalkylene glycols and their ethers and esters are given in British Pat. Specification No. 1,055,641. Other suitable lubricity agents are orthophosphate or sulphate salts of primary or secondary aliphatic amines having a total of from 4 to 24 carbon atoms, dialkyl citrates having an average of from 3% to 13 carbon atoms in the alkyl groups, aliphatic dicarboxylic acids and esters thereof, specific examples being Diamylamine orthophosphate Dinonylamine orthophosphate Diamylamine sulphate Dinonyl citrate Di(2-ethyl hexyl)citrate Polyoxyethylene sebacate derived from a polyoxyethylene glycol of M.W.20O

Polyoxyethylene azelate derived from a polyoxyethylene glycol of M.W.200

Polyoxyethylene adipate derived from a polyoxyethylene glycol of M.W.200

Polyoxyethylene/polyoxypropylene glutarate derived from mixed polyoxyglycols of average M.W. of about 200 Glutaric acid Azelaic acid Sebacic acid Succinic acid Di ethyl sebacate Di 2-ethyl hexyl sebacate Di iso octyl azelate Unsaturated aliphatic acids or their salts may also be used e.g. oleic acid or potassium ricinoleate.

Corrosion inhibitors which may be used in the present invention may be selected from heterocyclic nitrogen containing compounds, e.g. benzotriazole and benzotriazole derivatives such as those described in British Pat. Specification No. 1,061,904 or mercapto benzothiazole. Many amines or derivatives thereof are also suitable as corrosion inhibiters, for example di n-butylamine di n-amylamine cyclohexylamine morpholine triethanolamine and soluble salts thereof e.g. cyclohexylamine carbonate.

Phosphites are also good corrosion inhibitors e.g.

Tri phenyl phosphite Di isopropyl phosphite and certain inorganic salts may be incorporated e.g. so dium nitrate.

Other additives which may be included are antioxidants such as diarylamines e.g. diphenylamine, p,pdioctyl-diphenylamine, phenyl-a-naphthylamine or phenyl-B-naphthylamine. Other suitable antioxidants are those commonly known as hindered phenols which are exemplified by 2,4-dimethyl-6-t-butyl phenol 2,6-di-tbutyl-4-methyl phenol 2,6-di-t-butyl phenol l,l-bis (3,5-di-t-butyl-4-hydroxyphenyl)-methane 3,3',5,5"tetra-t-butyl 4 4 dihydroxy-diphenyl 3-methyl-4,6-di-t-butyl phenol 4-methyl-2-t-butyl phenol Yet further additives which may be used are phenothiazine and its derivatives, for example those having alkyl, or aryl, groups attached to the nitrogen atom or to the aryl groups of the molecule.

Other additives which may be used include alkylene oxide/ammonia condensation products as corrosion inhibitor, for example the propylene oxide/ammonia condensation product described in U.K. Pat. Specification No. 1249803. Further lubricity additives which may be used are complex esters, such as that sold under the trade name Reoplex 641 and also described in U.K. Specification No. 1249803. Moreover, long chain (e.g. C primary amine corrosion inhibitors and polymerised quinoline resin antioxidants, as described in Specification No. 1249803, may be used, examples of such amines and resins being the commercially available materials Armeen 12D and Agerite resin D respectively.

Conventional additives such as those hereinbefore described are normally employed in small amounts such as 0.5 to for example, 0.1 to 2% by weight.

As hereinbefore stated the fluids of the presentinvention may contain conventional hydraulic fluid additives, including corrosion inhibitors such as amines and derivatives thereof. We have now found that certain amines are also useful in the hydraulic fluids for a different purpose. In particular these amines suppress a tendency for the borate esters in the hydraulic fluid to precipitate boric acid in service, the 'boric acid being derived from hydrolysis in the presence of absorbed atmospheric moisture.

The amines which are particularly useful for stabilising the hydraulic fluids, i,e, suppressing boric acid precipitation, are aliphatic amines and certain aromatic amines. Accordingly, in a preferred aspect of the invention the fluids contain an aliphatic amine, more preferably a primary or secondary aliphatic amine. It is especially preferred to use a primary or secondary aliphatic amine containing from 4 to 12 carbon atoms, e.g. nbutylamine, n-laurylamine or n-octylamine. As hereinbefore stated certain aromatic amines may be used. in a non-preferred embodiment, in place of the aliphatic amines. Examples of the aromatic amines include diphenylamine, phenyl hydrazine, p-phenylene diamine and o-,mor p-aminophenol.

The amine stabilisers may be used in an amount of from 0.1 to 5%, preferably from 0.5 to 3%, by weight based on the total weight of the hydraulic fluid.

It will be understood that mixtures of the borate esters hereinbefore described may be employed in the present invention. Moreover mixed" esters may be used, i.e. esters derived from 2 or more different glycol monoethers. Such mixed" esters will contain 2 or more different glycol monoether residues in each molecule and it may be that ester interchange may take place to a greater 'or lesser degree, i.e. transference of glycol monoether residues from one boron atom to another may occur so that different borate esters are formed in service. The resulting mixture of borate esters will, of course, be indistinguishable from mixtures formed by blending of the separate esters in the appropriate amounts, hence the use of such mixtures in hydraulic fluids is included in the present invention.

In another aspect of the present invention there is provided a hydraulic system containing the hydraulic fluids of the present invention. ln a further aspect there is provided a method of transmitting lower. which method comprises introducing the hydraulic fluids of the present invention into a hydraulic system and trans mitting power by applying pressure thereto.

The invention will now be illustrated with reference to the following examples.

EXAMPLE 1 Methyl diethylene glycol ethyl diethylene glycol methyl triethylene glycol borate was prepared by refluxing 2 moles of orthoboric acid with 2.2 mole of triethylene glycol monomethyl ether for 3 hours in a Dean and Stark apparatus in the presence of 200 ml. toluene as a water entrainer. After the evolution of 35 ml. of water, 2.2 mole of diethylene glycol monoethyl ether was added and refluxing continued for 5 hours until a further 36 ml. of water was evolved. Thereafter 2.2 mole of diethylene glycol monomethyl ether was added and refluxing continued for 6 hours until 36 ml. of water was evolved. After completion of the esterification, toluene and excess glkycol ether were stripped off (7 /2/mm/Hg. 100C.) to produce the methyl diethylene glycol ethyl diethylene glycol methyl triethylene glycol borate (Yield 774g. 91%) which has a SAE equilibrium reflux Boiling Point of 327C. and a viscosity of 889 cSt. at 40C.

Humidity tests were carried out on blends of this borate ester with dicarboxylic acid esters by placing mls. of the fluid being tested in a 250 ml. beaker and leaving for 6 hours in an environmental cabinet at Relative Humidity and F. The boiling point of the fluid was determined before and after treatment in this manner, the drop in boiling point indicating the effect of humidity on the test fluids.

The fluids tested and the results obtained were as follow:

Fluid Initial B.Pt.(C) Final B.Pt.(C)

100% borate cstcr 327 I49 50% boratc ester 50% DMDGN 329 I56 457: boratc ester 45% DMDGN 306 145 i071 monocthyl ether of tricthylenc glycol.

DMDGN was the dHmonoethyl ether of diethylene EXAMPLE 8 glycol) nylonate described in U.K. Pat. Specification No. 1.083.324. TECDA 48 l l 8 Further examples of fluids in accordance with the Borgia B 49 gi present invention were formulated as in the following r 8l R 3 parts examples 2 to 22, in which all parts are by weight: Bcnzmriflmlc Parts TEGDA was the diacetate of triethylene glycol and EXAMPLE 2 Primene 81-R was a commercially available mixture of tertiary alkyl primary amines containing from 12 to 14 carbon atoms. DMDGN 48 parts TEGDP 42 parts Boratc A 10 parts EXAMPLE 9 Di-amylaminc 0.5 parts TEGDP was the dipropionate of triethylene glycol TEGDP 50 r s and Borate A was tris (monomethyl ether of triethylene A 50 Parts Armccn 10D 1.0 parts glycol) borate.

Armeen 10D was a commercially available distilled EXAMPLE 3 grade of primary amine consisting of about 90% ndecylamine, 4% n-octylamine and 6% n-dodecylamine. DMDGN 15 parts 'IEGDP parts EXAMPLE l0 Boratc A 50 parts Di-n-hcxylaminc l.() parts 35 Boratc A 63.5 parts TEGDP 35.0 parts Armeen 10D 1 5 parts EXAMPLE 4 Benzotriazole Oil parts DMDGN 32 parts EXAMPLE ll TEGDP 38 parts 40 Borate A 30 parts n-Octylaminc 0.7 parts Borutc C parts DMDGN 40 parts TEGDP 15 parts EXAMPLE 5 45 Octylamine 0.7 parts Borate C was ethyl diethylene glycol methyl diethyl- DMDGN 52 parts ene glycol methyl triethylene glycol borate. TEGDP 37 parts Boratc B l() parts Di-n-hcxylaminc 1.0 parts EXAMPLE l2 Agcritc Resin D 0.3 parts Borate B was tris (monomethyl ether of diethylene Boratc D 30 parts glycol) borate. DMDGN 30 Parts TEGDP 35 parts 55 Primcne 8l-R 1.0 parts EXAMPLE 6 Borate D was bis methyl triethylene glycol methyl dieth lene l col borate. DMGN 52 parts y g y TEGDP l7 parts Borutc B 30 parts Octyluminc 11) parts EXAMPLE Agcritc Rcsin D 0.5 parts Borate E 20 parts EXAMPLE 7 DMDGN 45 parts TEGDP 35 parts Di'hcxylamine l.0 parts DMDGN 49 parts B 't B 49 t. o liiiliminc z 52: Borate E was tris (monoethyl ether of methylene gly- Agcrite Resin D 0.5 parts (:01) borate.

EXAMPLE 14 Burutc F 15 parts DMDGN 60 parts TEGDP 25 parts Di-amylaminc 1.0 parts Borate F was tris l-butoxy ethoxy 2 propanol) borate.

EXAMPLE l5 Boratc G 20 parts DMDGN 70 parts TEGDP parts Di-amylaminc 110 parts Borate G was tris (monobutyl ether of diethylene glycol) borate.

EXAMPLE 1 6 Bo ratc H 25 parts DMDGN 40 parts TEGDP 35 parts Oetylaminc 0.7 parts Borate H was bis ethyl triethylene glycol isopropyl triethylene glycol borate.

EXAMPLE 1 7 Di-(monomethyl ether of dicthylenc glycol) adipatc 60 parts Borate A 30 parts TEGDP 10 parts Armccn 12 D 0.5 parts Armeen 12 D was a commercially available distilled grade of primary amine consisting of about 95% ndodecylamine. 2% n-decylamine and 3% ntetradecylamine.

EXAMPLE l8 Di-(monocthyl ether of tricthylcnc glycol) succinutc 30 parts Boratc A 40 parts 'lliGDP 30 parts Di-umyluminc 1.0 parts EXAMPLE 19 Di-(monomcthyl ether of propylene glycol) succinatc 30 parts DMDGN 20 parts TEGDP 20 parts Boratc A 30 parts Di-hcxylamine 1.0 parts EXAMPLE 20 Di(mono-ipropyl ether of diethylcnc glycol) adipatc 30 parts Borate A 40 parts DMDGN parts T5601 15 parts Octylaminc 1.0 parts EXAMPLE 21 Di(monomcthyl ether of dicthylcnc glycol) azelate 60 parts Borate A 30 parts TEGDP 10 parts Armcen [0D 1.5 parts EXAMPLE 22 Di-(monoethyl ether of tricthylcnc glycol) schacatc 20 parts DMDGN 20 parts Boratc A 30 parts TEGDP 30 parts Primene 8l-R 2.0 parts In order to illustrate the properties of the hydraulic fluids of the present invention the foregoing blends 2 to 22 were tested using a variety of standard testing procedures. The results of these tests showed that the blends were useful hydraulic fluids, particularly for use in hydraulic brake and clutch systems. For example, blends 2. 3 and 4 using the same ester components in varying proportions all fully satisfy the requirements of the SAE 11703 b specification for high quality heavy duty hydraulic fluids, and also satisfy the stringent corrosion requirements of the Ford ESA-M6C-100l-A specification. Other blends also fully satisfied the SAE 11703 b specification, or the slightly revised SAE J 1703 c specification introduced during the period when the blends were being tested. For example blend 10, in which the carboxylate ester component consisted entirely of esters in accordance with Formula II. fully satisfies the requirements of the SAE J1703 c specification.

The test also revealed that the properties of the blends were not a simple compromise between the desirable high temperature properties of the borate ester component and the desirable low temperature properties of the carboxylate ester component. On the contrary the tested blends showed that both low and high temperature properties were retained to an unexpectedly large extent, in some case there being substantial complete retention of desirable properties at both high and low temperatures. In particular the blends in accordance with the present invention had good boiling points, vapour lock temperatures and low temperature viscosity properties. Furthermore, these properties do not deteriorate unduly even in the presence of substantial quantities of water. During the service life of a hydraulic brake fluid moisture is absorbed from the atmosphere and this impairs the properties of the fluid. If the properties are impaired to too great an extent the operating efficiency of the hydraulic system containing the fluid is seriously reduced. It is therefore extremely important that the properties of a hydraulic brake fluid do not deteriorate unduly in the presence of water.

The low temperature viscosity properties of the fluids of the present invention were tested by determining the viscosity at 40C in accordance with the procedure set forth in the SAE 11703 specification, the viscosity being determined for dry samples of the tested fluids and also for samples to which known quantities of water had been added. The results are set out in the following Table 1.

The boiling point of the tested fluids were determined by the procedure set out in the SAE .ll703 specification, the boiling point being determined for dry samples of the tested fluids and also for duplicate samples of the fluid after being subjected to a D.O.T. Humidity test according to the procedure set forth in the F M V S S 116 specification. Briefly, the humidity test is carried out by enclosing one sample of the test fluid in each of two dessicators and one sample ofa standard reference fluid in each of a further two dessicators, there being an aqueous slurry of ammonium sulphate in each dessicator which provides an atmosphere of 8071 Relative Humidity. The samples are kept in the dessicator until the reference fluid absorbs 3.571 by weight of water. The results obtained are set out in the following Table 2.

The vapour lock temperatures of the tested fluids were determined using an apparatus comprising a substantially spherical glass bulb having a hollow, volumetrically calibrated, cylindrical projection extending vertically from the top of the bulb, the projection being sealed at its upper end. A glass tube extends laterally from the bottom of the bulb and further extends vertically alongside the bulb, before terminating in a funnel. The bulb is completely filled with the test fluid via the funnel and glass tube so that no air bubbles remain in the bulb. The bulb is then completely submerged in a heating bath filled with a transport fluid through which the calibrated section of the apparatus can be viewed 10 ter.

In a similar manner the results set out in Tables 2 and 3 show that the high temperature properties of the fluids of the present invention are comparable with the high temperature properties of fluids based on borate l5 esters, without carboxylate esters present, whereas fluids based on carboxylate esters without borate esters are known to have relatively poor high temperature properties.

The rubber swell test results set out in Table 4 show the fluids of the present invention may be blended so as to comply with the commonly accepted standards required by such specifications as the SAE J1703 specification.

TABLE 1 Low Temperature Viscosity Properties and the temperature of the bath is gradually increased. T95! Blend Vis sity at 0C(cSt) Dry 1'7: water 2% water 371 water 5% water When any vapour formatlon occurs, thls vapour accumulates in the calibrated section of the apparatus and 3 Examplu 3 1727 I777 I837 Exam le 3 1737 1735 1994 2255 the temperature at which pre-selected quantltles of Example 4 1766 1737 9 2032 vapor accumulate can be determined. The following g s"; {ggi am 0 Table 3 sets out the results obtalned 1n thls test for dry E l 7 1427 7 1775 2019 c t a 180 a w S 16 st Example 8 1252 1206 1342 1557 samples of tes fluld nd a for et amp of te Example 9 1208 1267 I498 168] fluld formed by mlxlng the dupllcate samples of the test Exam le 10 1370 1470 1710 1760 Exam le 11 1501 1633 1808 1990 2277 fluld whlch had been used In the bolllng polnt determl Example 12 1686 1708 1783 1899 2058 nations after the D.O.T. Humldlty tests. Exam le 13 1831 1886 1843 1964 2124 Example 14 1980 2374 The Rubber Swell propertles of the test flulds were Example 5 2290 2173 2638 3004 also determined according to the procedure set forth 1n Exam le 16 1882 1912 1961 2069 2220 Example 17 1874 2031 2266 2474 the SAE J1703 speclflcatlon. The results obtalned are Example 18 3233 3264 3532 4 set out in the following Table 4. Example 19 2084 2514 E l 20 2059 2069 2338 The results set out m Table 1 show that the flulds 1n 323 3] 2358 2351 3541 3042 accordance with the present inventlon are of the same Example 22 2439 6 2599 3048 TABLE 2 Boiling Points Before and After D.O.T. Humidity Test Best Blend Boiling Point (C) Dry Wet (Sample A) Wet (Sample B) Mean Water (A+B) Content (7: by wt) Example 2 312.5 200 192 196 2.19 Example 3 309 196 199 197.5 3.74 Exam le 4 311 182 193 187.5 3.23 Example 5 299 164 173 168.5 2.86 Example 6 299 181 187 184 3.60 Example 7 310 202 209 205.5 4.43 Exam le 8 273.5 182 191 186.5 4.52 Example 9 307 205 204 204.5 3.66 Example 10 311 213 3.77 Exam le 11 305 188 205.5 197 3.94 Example 12 302 193 180 186.5 3.84 Example 13 305 192 194 193 3.02 Example 14 315 197 202 199.5 2.16 Example 15 309 199 200 199.5 2.60 Example 16 307 179 180 179.5 2.75 Example 17 299 193 3.37 Example 18 306 204 3.35 Example 19 294 192.5 3.24 Exam le 20 297 190.5 3.42 Exam le 21 307 201.5 3.22 Example 22 302 3.15

Not recorded.

TABLE 3 Vapour Lock Temperatures Before and After D.O.T. Humidity Test Vapour Lock Temperatures (C)-Dry Vapour Lock Temperature Best Blend (C)-combined duplicate wet samples 0.4 ml 0.4 ml

vapour 1.0 ml 3.0 ml 5.0 m1 vapour 1.0m! 3.0m1 5.0m]

Example 2 299 157 158 160 163 Example 3 300 167 171 174 175 Example 4 311 154 158 162 165 Example 5 280 140 145 150 155 Example 6 294 164 165 170 173 Example 7 301 180 180 184 186 Example 8 273 163 167 171 173 Example 9 305 170 173 176 178 Example 10 290 292 297 300 178 182 186 188 Example 11 276 280 284 286 164 167 173 176 Example 12 280 284 288 290 161 164 166 168 Example 13 278 282 286 289 145 150 152 154 Example 14 278 283 288 291 154 157 160 162 Example 15 295 299 302 305 155 158 161 162 Example 16 293 296 299 301 147 151 153.5 155 Example 17 273 278 285 288 152 160 164 165 Example 18 286 290 295 297 167 170 173 174.5 Example 19 272 277 280 281 152 155 159 160 Example 20 295 299 302 304 160 162 165 167 Example 21 293 297 300 303 154 157 158 161 Example 22 288 289 293 296 154 156 159 161 Not recorded TABLE 4 Rubber Swell Properties (Effect on SBR cups) Effect on SBR cups (120 hours at 70C) BEST BLEND (70 hours at 120C Effect on SBR cups Base diameter Hardness Base diameter Hardness increase (mm) decrease Increase [mm] decrease (points) (points) Example 2 0.9 Nil 127 3 Example 3 1.08 5 1.35 5 Example 4 0.94 10 1.28 8 Example 5 0.96 10 1.30 6 Example 6 0.86 9 1.32 5 Example 7 1.02 7 1.22 4 Example 8 1.21 5 1.69 10 Example 9 1.10 10 1.59 7 Example 10 0172 3 1.34 8 Example 11 1.34 4 Example 12 1.18 6 Example 13 1.38 7 Example 14 1.80 5 Example 15 1.47 5 Example 16 1.46 5 Example 17 0.89 4 Example 18 1.05 2 Example 19 1.51 7 Example 20 1.45 Example 21 1.44 13 Example 22 1.40 1! We claim: ylene group and a butylene group, each n is the same 1. A hydraulic fluid consisting essentially of from 10 to 90% by weight of at least one ester having a general formula selected from the groupconsisting of: A

R and or different and is selected from the group consisting of O and an integer of from 1 to 3, each R is the same or different and is selected from the group consisting of an ethyl group and a methyl group, each R is the same or different and is selected from the group consisting of an ethylene group and a propylene group and m is an integer such that the total number of carbon atoms in the (R O9 group is from 4 to 12, and from 10 to by weight of at least one borate ester having the general formula wherein each R is the same or different and is selected from the group consisting of straight chain alkyl groups containing from 1 to 4 carbon atoms and branched chain alkyl groups containing from 1 to 4 carbon atoms, each R is the'same or different and is an alkyl group containing from 1 to 8 carbon atoms and each p is the same or different and is an integer of from 1 to 8. r

2. A hydraulic fluid according to claim 1 wherein each R contains from 1 to 4 carbon atoms and each integer p is from 1 to 4.

3. A hydraulic fluid according to claim 1 wherein the total of the three integers p is from 5 to 15.

4. A hydraulic fluid according to claim 1 additionally comprising from 0.1 to 5% by weight of an amine selected from the group consisting of primary aliphatic amines containing from 4 to 12 carbon atoms, secondary aliphatic amines containing from 4 to 12 carbon atoms. diphenylamine, phenyl hydrazine, p-phenylene diamine, o-aminophenol, m-aminophenol and paminophenol.

5. A hydraulic fluid as claimed in claim 1 wherein the borate ester is selected from the group consisting of tris methyl triethylene glycol borate; tris ethyl triethylene glycol borate; tris methyl diethylene glycol borate; tris ethyl diethylene glycol borate; methyl diethylene glycol ethyl diethylene glycol methyl triethylene glycol borate; butyl diethylene glycol or his butyl diethylene glycol borates in which the, or each, group OR""],,OR not derived from the monobutyl ether of diethylene glycol is derived from the monomethyl or monoethyl ether of dior tri-ethylene glycol; and alkyl glycol or bis alkyl glycol borates in which the, or each, group OR OR not derived from a monoalkyl ether of a monoglycol is derived from the monomethyl or monoethyl ether of dior tri-ethylene glycol.

6. A hydraulic fluid according to claim 1 comprising borate ester in an amount of from 2 to by weight. 

1. A HYDRAULIC FLUID CONSISTING ESSENTIALLY OF FROM 10 TO 90% BY WEIGHT OF AT LEAST ONE ESTER HAVING A GENERAL FORMULA SELECTED FROM THE GROUP CONSISTING OF:
 2. A hydraulic fluid according to claim 1 wherein each R6 contains from 1 to 4 carbon atoms and each integer p is from 1 to
 4. 3. A hydraulic fluid according to claim 1 wherein the total of the three integers p is from 5 to
 15. 4. A hydraulic fluid according to claim 1 additionally comprising from 0.1 to 5% by weight of an amine selected from the group consisting of primary aliphatic amines containing from 4 to 12 carbon atoms, secondary aliphatic amines containing from 4 to 12 carbon atoms, diphenylamine, phenyl hydrazine, p-phenylene diamine, o-aminophenol, m-aminophenol and p-aminophenol.
 5. A hydraulic fluid as claimed in claim 1 wherein the borate ester is selected from the group consisting of tris methyl triethylene glycol borate; tris ethyl triethylene glycol borate; tris methyl diethylene glycol borate; tris ethyl diethylene glycol borate; methyl diethylene glycol ethyl diethylene glycol methyl triethylene glycol borate; butyl diethylene glycol or bis butyl diethylene glycol borates in which the, or each, group -OR5)pOR6 not derived from the monobutyl ether of diethylene glycol is derived from the monomethyl or monoethyl ether of di-or tri-ethylene glycol; and alkyl glycol or bis alkyl glycol borates in which the, or each, group -OR5)p OR6 not derived from a monoalkyl ether of a monoglycol is derived from the monomethyl or monoethyl ether of di- or tri-ethylene glycol.
 6. A hydraulic fluid according to claim 1 comprising borate ester in an amount of from 2 to 60% by weight. 